Executable code for a data processor such as a microcontroller, requires testing and correction during its development cycle. Software debugging is initially done in a simulator or debugger offline. Once the software is debugged, it is then down loaded into the target system. However, if the software does not work correctly, for example, due to a timing problem it is then necessary to do an "in circuit" examination of the software and the data that it is manipulating. It is known to perform this be removing the target data processor and replacing it with a replica of the data processor which can be probed or interrogated via an emulation pod. The replica data processor emulates the real data processor and this process is called "in circuit emulation".
A disadvantage of known "in circuit" emulators is that the additional sockets, clips, adaptors or pods can induce extra parasitic components into the target system which alter its performance. This usually restricts the emulation to a slow speed in order to avoid timing problems introduced by the parasitic components. The use of such in circuit emulators can cause problems where debugging is to be performed in hybrid digital-analogue systems where analogue accuracy is a critical issue, especially when more than 6 or 7 bit resolution of analogue variables is used.
It was also known, in the case of microcontrollers where the internal address and data busses do not come out to the pins of the data processor, to produce a special "bond-out" version of the circuit. This has to be manufactured into a bigger package to bring these extra signals to the pins so that the emulator can monitor them. The bond-out version is disadvantageous since it requires the chip manufacturer to create a second version of the chip and package, with consequent timing differences from the read chip, increases complexity, and a need to provide an adaptor for connecting the "bond-out" version of the chip to target systems in place of the standard chip package.
It is known to integrate emulation address comparators and emulation break point registers within an integrated circuit and then to perform a hardware compare of the contents of the address resister with the emulation break point register in order to determine when to force a break point for emulation purposes. However, the additional registers and comparators are wasteful of space on the silicon die of the integrated circuit, and are inflexible in their operation. An additional register and comparator is required for each break point. Typically a designer may wish to have between eight and sixteen break points available. The addition of sixteen or so additional registers and comparators can add a significant cost to the production cost of the integrated circuit.